1. Field of the Invention
The present invention generally relates to methods and apparatus for analyzing documents. This invention more specifically relates to methods and apparatus for verifying the authenticity of a document by processing and analyzing reflected light which is collected from the document.
2. Background Information
Devices have been known for testing the presence of color in paper securities, for checking bank notes, for validating currency, for optical recognition of patterns on documents, and for generally distinguishing between authentic and counterfeit documents. It has been known to provide such devices in various ways.
U.S. Pat. No. 4,183,665 provides a device for determining whether a document has color in it. Filters for this device are chosen to detect if a specific color is present on the document in question. Verification of authenticity for this device requires the personal judgment of the user as to which colors are present on the document.
U.S. Pat. No. 5,537,486 teaches a device which is stated to be a high-speed document verification system. It is primarily designed to detect fine patterns which may not be reproduced by copying equipment.
U.S. Pat. No. 4,204,765 teaches an apparatus for testing colored securities. This device uses different colored diodes for illumination to determine if color is present in a tested document.
U.S. Pat. No. 4,184,081 teaches a method for checking banknotes and apparatus therefor. This patent provides an instrument for measuring color which initiates its analysis on the premise that the color of the copy will not appear exactly the same as the color of the original.
U.S. Pat. No. 4,319,137 teaches an apparatus for identifying sheet like printed matters. The device of this patent is directed to black an recognition.
U.S. Pat. No. 4,587,434 is provided as a currency note validator. This device utilizes a narrow band LED illumination to measure responses of a currency note to a specific portion of the spectrum.
U.S. Pat. No. 3,679,314 teaches an apparatus for optically testing the genuineness of banknotes and other tokens of value. This device uses several narrow band light sources and receives and analyzes the light that is transmitted through the document.
U.S. Pat. No. 3,220,540 teaches a method and apparatus for discriminating between xe2x80x9cdesiredxe2x80x9d and xe2x80x9cundesiredxe2x80x9d documents. This device uses several narrow band light sources and takes measurements on several areas of a target document.
U.S. Pat. No. 3,480,785 provides a method and apparatus for validating documents by spectral analysis of light reflected therefrom. This device employs a comparison of measured values in relationship to each other for validation.
U.S. Pat. No. 5,027,415 is provided as a bill discriminating device which uses two narrow band detectors and a ratio comparison of values measured in testing to verify the authenticity of documents tested.
U.S. Pat. No. 4,618,257 is a color sensitive currency verifier which uses two sensors augmented with filters to analyze narrow band width spectral readings on a target. Validation of authenticity occurs by a comparison of the difference between the two measurements.
U.S. Pat. No. 5,498,879 teaches an apparatus for optical recognition of documents by photoelectric elements having vision angles with different length and width. This device uses several narrow band sensors over a linear strip of the document to measure different reflective values of the light in those particular areas.
U.S. Pat. No. 4,204,765 discloses an apparatus for testing color securities. This device uses narrow band light sources to provide reflective light.
Humans are considered to have a tristimulus system, which means that they have three types of color sensors which are sensitive to different weighted portions of the visible spectrum. However, the exact mechanism for color vision is not completely understood due to the difficulty of analyzing the effects of the neural network of the brain as the these effects relate to the retina-brain connection. In lieu of the exact mechanism of color perception, a set of weighting functions was derived from a color matching experiment and adopted as a standard observer by Commission Internationale de l""Eclairage (CIE). Three spectral weighting functions in particular comprise the tristimulus CIE standard observer, which can be employed as a model of human color perception.
A person is generally unaware of these three individual responses to a color object, and instead senses a composite effect of the three stimuli. This behavior of human color perception permits different spectral distributions to appear identical to a human observer. For example, a broad spectrum of light reflected from an object may be interpreted by a human visual system to be white, but the proper blend of red, blue, and green colors will also appear white to the human observer. These two spectrums have different spectral compositions, but they both may be perceived by a human observer to have identical color appearances. Unfortunately, this error in judgment is a boon to those who illegally profit from the reproduction of certain documents such as currency.
Conventional production techniques can produce a first document which has colors which appear to a human observer to be the same as the colors in a second, similar document. However, if the same coloring process was not employed to produce these documents, then the documents are susceptible to differentiation. To a human observer, though, the colors of the first document can appear identical to the colors of the second document. Employing broadband spectral analysis can demonstrate the differences in the colors of these documents.
Conventional use of spectral analysis has been limited to devices which utilize relatively narrow color bands to differentiate between authentic documents and their counterpart reproductions. As a result, an apparatus and method are needed which can be applied for broadband spectral analysis on a wide variety of documents.
What is needed then is a document authentication method and apparatus which use a light source to obtain a broad spectrum of reflected light from a document. A more effective and thorough normalizing of the light analyzed is also needed to verify the authenticity of a variety of documents. In addition, a consistently accurate method and apparatus for comparing the spectral signature generated by a test document to a previously programmed target document is needed.
The method and apparatus for verifying authenticity of a document of the present invention have satisfied the above-mentioned needs as well as others.
The method of the present invention provides the initial step of providing a broadband light source and illuminating a portion of a document to be verified with the broadband light source. This generates reflected light from the document. The method then provides for collecting and analyzing the reflected light by converting it into a corresponding electrical signal or signals. Next, the electrical signal or signals are digitized to form an array. The method can then include normalizing this array to develop and store a spectral signature associated with the document. The method of the present invention then provides for comparing a test document spectral signature to the spectral signature of a previously stored document. This comparison of the test document spectral signature to the previously stored spectral signature can be accomplished by using a matching function to determine authenticity.
The apparatus of the present invention may include an enclosure having a transparent opening disposed therein. A broadband light source is provided to illuminate a portion of a document placed on the transparent opening. The apparatus may employ a collection lens and optical fiber to receive and transfer light received from the illuminated document. This reflected light is then transferred to an aperture which is located at the focal point of a collimating lens. The collimating lens functions in conjunction with a diffraction grating, or another suitable spectral spreading device, to provide a spectrum of light wavelengths to a photosensor device. A microcontroller or conventional microprocessor and additional components can then be employed in conjunction with the apparatus to perform storage and authenticity determination functions for tested documents. In another aspect of the present invention, several steps of the process may be condensed into the functionality of a single optical component.
Accordingly, it is an object of the present invention to provide a document analysis method and apparatus which utilize a broader range of wavelengths to provide a more thorough analysis in determining document authenticity.
It is a further object of the present invention to provide an apparatus which may be produced at an economical cost.
It is a still further object of the present invention to provide a document analysis method and apparatus which reduce the inherent variation introduced into the analysis by soiled or faded documents which are tested.
These and other objects of the invention will be more fully understood from the following description on reference to the illustrations appended hereto.